U.S. patent number 5,282,386 [Application Number 07/949,165] was granted by the patent office on 1994-02-01 for apparatus and technique for fluid level determination in automatic transmissions.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Ronald A. Lee, Phillip F. McCauley, William M. Murray, Robert T. Niemczyk, Thomas H. Wilson.
United States Patent |
5,282,386 |
Niemczyk , et al. |
February 1, 1994 |
Apparatus and technique for fluid level determination in automatic
transmissions
Abstract
An apparatus and technique for fluid level determination in
automatic transmissions. The invention employs an electronic
control unit in association with an automatic transmission for a
vehicle, the electronic control unit receiving data corresponding
to transmission oil level, transmission oil temperature, engine
speed, transmission speed, and transmission selected range. Upon
determining that such data satisfies certain diagnostic tests, the
level of transmission fluid within the transmission is determined
and adjusted or otherwise normalized to ideal test conditions. The
electronic control unit compensates an oil level signal for
deviations in oil temperature from an optimum test temperature, and
makes further compensation for deviations in engine speed and
settling time at the time that the test data is acquired.
Additionally, variations in oil density as a function of oil
temperature are also compensated.
Inventors: |
Niemczyk; Robert T.
(Indianapolis, IN), Wilson; Thomas H. (Indianapolis, IN),
McCauley; Phillip F. (Zionsville, IN), Lee; Ronald A.
(Brownsburg, IN), Murray; William M. (Pittsboro, IN) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25488679 |
Appl.
No.: |
07/949,165 |
Filed: |
September 22, 1992 |
Current U.S.
Class: |
73/292; 340/459;
374/142 |
Current CPC
Class: |
F16H
59/72 (20130101); G01F 23/804 (20220101); F16H
57/0447 (20130101); F16N 29/00 (20130101); F16N
2200/10 (20130101); F16N 2250/16 (20130101); F01M
2250/64 (20130101); F16N 2260/04 (20130101); B60W
2050/021 (20130101); F16H 2061/1208 (20130101); F16N
2200/12 (20130101); F16N 2270/10 (20130101); F16H
57/0449 (20130101); F16N 2250/18 (20130101) |
Current International
Class: |
F16H
63/40 (20060101); F16H 63/00 (20060101); F16H
59/72 (20060101); F16N 29/00 (20060101); G01F
23/00 (20060101); F16H 61/12 (20060101); B60K
041/04 (); G01F 023/30 () |
Field of
Search: |
;73/292 ;374/142
;340/450,450.3,449,459 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yasich; Daniel M.
Attorney, Agent or Firm: Scherer; Donald F.
Claims
What is claimed is:
1. A method for determining an oil level in a transmission driven
by an engine, comprising:
generating a first signal corresponding to an actual transmission
oil level and density;
generating a second signal corresponding to actual transmission oil
temperature;
determining said actual oil level as a function of said first and
second signals;
determining a deviation of actual engine speed from a reference
idle engine speed and compensating said determination of actual oil
level as a function thereof;
calculating a deviation of said compensated actual oil level from a
desired oil level and determining a volume error therefrom;
determining a deviation of said actual oil temperature from a
typical operating reference temperature of said transmission oil;
and
adjusting said volume error as a function of said deviation of said
oil temperature.
2. A method for determining an oil level in a transmission driven
by an engine, comprising:
placing said transmission in neutral;
determining an actual oil level within the transmission;
determining a deviation of actual engine speed from a reference
idle engine speed and compensating said determination of actual oil
level as a function thereof;
determining a period of time from when said transmission was placed
in neutral and said determination of actual oil level was made and
compensating said determination of actual oil level as a function
thereof;
calculating a deviation of said compensated oil level determination
from a desired oil level and determining a volume error
therefrom;
determining a deviation of actual oil temperature from a typical
operating reference temperature of the transmission oil; and
adjusting said volume error as a function of said deviation of said
oil temperature.
3. Apparatus for determining an oil level in a transmission driven
by an engine, comprising:
means within the transmission for generating a first signal
corresponding to an actual transmission oil level and density;
means within the transmission for generating a second signal
corresponding to actual transmission oil temperature; and
means connected to said transmission for receiving said first and
second signals and determining said actual oil level as a function
thereof, determining a deviation of actual engine speed from a
reference idle engine speed, determining a period of time between
when the transmission is placed in neutral and said determination
of actual oil level is made, compensating said determination of
actual oil level as a function of said deviation of engine speed
and said period of time, calculating a deviation of said
compensated oil level from a desired oil level and determining a
volume error therefrom, determining a deviation of actual oil
temperature from a typical operating reference temperature of the
transmission oil, and adjusting said volume error as a function of
said deviation of oil temperature.
Description
TECHNICAL FIELD
The invention herein resides in the art of power transmission
systems and, more particularly, to automatic transmissions for
vehicles. Specifically, the invention relates to an apparatus and
technique for accurately and reliably determining the transmission
oil level in automatic transmissions for vehicles.
BACKGROUND ART
Automatic transmissions for vehicles are in common use, for they
are particularly conducive to vehicle efficiency and operator
comfort. However, the operational efficiency of an automatic
transmission is, in large part, dependent upon the presence of a
proper volume of transmission fluid or oil within the transmission
itself. Not only is the proper operation of the transmission
dependent upon the presence of an appropriate volume of
transmission oil, but the same also assures that transmission wear
is minimized, prolonging the useful life of the system.
Presently, the fluid level within an automatic transmission is
typically monitored through the use of a dipstick. However, for
correct fluid level measurement, the dipstick must be properly
calibrated for each installation, and the measurements must be
taken under optimum or ideal operating conditions. Included among
these conditions are an assurance that the transmission oil is at a
normal operating temperature, the engine speed or input speed to
the transmission is at a set level, and oil drain back or settling
time requirements for the transmission have been satisfied. Of
course, operator capabilities also impact the accuracy of the
reading taken with the dipstick, since any such measurement
requires that the operator correctly observe and interpret the
difference between the oil line and the full/add lines upon the
dipstick. Quite frequently, the requirements for ideal operating
conditions and operator capability are not met when the measurement
is taken and acted upon. The resultant incorrect automatic
transmission fluid level results in poor shift quality, inefficient
operation, operator discomfort, and reduced transmission life.
There is a need in the art for an apparatus and technique for fluid
level determination in automatic transmissions which automatically
accounts and adjusts for less-than-ideal checking conditions, and
removes subjective interpretation of measurements in determining
the proper deviation of the fluid level in automatic transmissions
from a standard acceptable level.
DISCLOSURE OF INVENTION
In light of the foregoing, it is a first aspect of the invention to
provide an apparatus and technique for fluid level determination in
automatic transmissions which accounts and adjusts for non-ideal
operating conditions at the time of measurement.
Another aspect of the invention is the provision of an apparatus
and technique for fluid level determination in automatic
transmissions which is substantially automatic and not given to
operator error.
A further aspect of the invention is the provision of an apparatus
and technique for fluid level determination in automatic
transmissions which accommodates variations in oil temperature and
resultant density, engine speed, and settling time.
Further aspects of the invention are attained by an apparatus and
technique for fluid level determination in automatic transmissions
which allows for highly accurate and repeatable measurements.
Yet additional aspects of the invention are attained by an
apparatus and technique for fluid level determination in automatic
transmissions which are easily implemented with presently existing
electronic control units for transmissions.
The foregoing and other aspects of the invention which will become
apparent as the detailed description proceeds are achieved by a
method for determining an oil level in a transmission driven by an
engine, comprising: generating a first signal corresponding to an
actual transmission oil level and density; generating a second
signal corresponding to actual transmission oil temperature;
determining said actual oil level as a function of said first and
second signals; determining a deviation of actual engine speed from
a reference idle engine speed and compensating said determination
of actual oil level as a function thereof; calculating a deviation
of said compensated actual oil level from a desired oil level and
determining a volume error therefrom; determining a deviation of
said actual oil temperature from a typical operating reference
temperature of said transmission oil; and adjusting said volume
error as a function of said deviation of said oil temperature.
Other aspects of the invention which will become apparent herein
are attained by a method for determining an oil level in a
transmission driven by an engine, comprising: placing said
transmission in neutral; determining an actual oil level within the
transmission; determining a deviation of actual engine speed from a
reference idle engine speed and compensating said determination of
said actual oil level as a function thereof; determining a period
of time from when said transmission was placed in neutral and said
determination of actual oil level was made and compensating said
determination of actual oil level as a function thereof;
calculating a deviation of said compensated oil level determination
from a desired oil level and determining a volume error therefrom;
determining a deviation of actual oil temperature from a typical
operating reference temperature of the transmission oil; and
adjusting said volume error as a function of said deviation of said
oil temperature.
Yet additional aspects of the invention which will become apparent
herein are attained by apparatus for determining an oil level in a
transmission driven by an engine, comprising: means within the
transmission for generating a first signal corresponding to an
actual transmission oil level and density; means within the
transmission for generating a second signal corresponding to actual
transmission oil temperature; and means connected to said
transmission for receiving said first and second signals and
determining said actual oil level as a function thereof,
determining a deviation of actual engine speed from a reference
idle engine speed, determining a period of time between when the
transmission is placed in neutral and said determination of actual
oil level is made, compensating said determination of actual oil
level as a function of said deviation of engine speed and said
period of time, calculating a deviation of said compensated oil
level from a desired oil level and determining a volume error
therefrom, determining a deviation of actual oil temperature from a
typical operating reference temperature of the transmission oil,
and adjusting said volume error as a function of said deviation of
oil temperature.
DESCRIPTION OF DRAWINGS
For a complete understanding of the apparatus and techniques of the
invention, reference should be made to the following detailed
description and accompanying drawings wherein:
FIG. 1 is block diagram of an automatic transmission adapted for
employing the concept of the invention;
FIG. 2 is a block diagram illustration of a transmission electronic
control unit in communication with various transmission sensors in
the structure of FIG. 1; and
FIG. 3 is a flow chart of the method of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to the drawings and more particularly FIG. 1, it can
be seen that an automatic transmission for a vehicle which is
adapted for employing the concept of the invention is designated
generally by the numeral 10. The transmission system 10 includes a
power input shaft 12 appropriately connected to an engine or other
appropriate power source (not shown), and an output shaft 14
appropriately connected to a driven member such as a wheel axle or
the like (not shown). Interposed between the input and output
shafts 12, 14 is an automatic transmission 16 which, as is well
known to those skilled in the art, includes a plurality of
hydraulically controlled gear stages. If desired, the transmission
16 may include a hydrodynamic retarder 18 interconnected with the
power output shaft 14 for purposes of braking the vehicle by
braking the output torque of the output shaft 14 by increasing the
load thereon.
An electronic control unit 20 is, in standard fashion,
interconnected with the transmission 16 and retarder 18 through a
data and control bus 22. Those skilled in the art will readily
appreciate that the electronic control unit 20 comprises one or
more dedicated microprocessors or other control units. The
electronic control unit 20 controls the operation of the
transmission 16 and retarder 18 in standard fashion, and is adapted
for two way communication therewith, obtaining operational data and
providing resultant controlling commands.
As shown in FIG. 2, according to the invention the electronic
control unit 20 communicates through the data and control bus 22
with a plurality of sensors and transducers to obtain operational
information for assistance in determining the transmission fluid
level according to the invention. As a portion of the invention, an
appropriate thermistor or other temperature sensor 24 is maintained
within the reservoir of the transmission 16 to produce an output
signal corresponding to the instantaneous temperature of the
transmission oil. Similarly received within the reservoir cavity of
the transmission 16 is an oil level sensor 26 which, as is known to
those skilled in the art, presents an output signal which is a
function of the actual level of oil within the reservoir and the
density of the oil. In a preferred embodiment of the invention, the
oil level sensor 26 comprises a Hall effect sensor operating upon a
float. Of course, other sensors may be employed in keeping with the
concept of the invention. Since the density of the transmission oil
changes with temperature, and since the float level of the sensor
26 is not only a function of actual fluid level, but also of the
density of the fluid, the output of the oil level sensor 26 is a
function of actual oil level and the oil density as impacted by the
oil temperature.
An engine speed transducer 28 is also interconnected with the
electronic control unit 20 and produces an output signal
corresponding to the instantaneous speed of the engine connected to
the input shaft 14. Of course, the engine speed transducer 28 may
typically be provided in operative interconnection with the input
shaft 12. A transmission speed transducer 30 is also interconnected
between the electronic control unit 20 and the output shaft 14 to
provide a signal corresponding to the instantaneous transmission
output speed as evidenced at the shaft 14.
With the electronic control unit 20 preferably comprising one or
more dedicated microprocessors, it is most desired that the input
signals thereto be digital signals, rather than analogue.
Accordingly, the sensors and transducers 24-30 may either be
selected to provide digital output signals, or a suitable analogue
to digital converter may be interposed between each of the sensors
and transducers 24-30 and the electronic control unit 20 to assure
that digital information is provided thereto.
The data obtained from the sensors and transducers as illustrated
in FIG. 2 is employed in the process of FIG. 3 to obtain reliable
and accurate data corresponding to the deviation from ideal of the
volume of transmission oil received and maintained within the
automatic transmission 16. The process is designated generally by
the numeral 32. Those skilled in the art will appreciate that the
oil level system will typically be enabled only when the vehicle is
stopped, the transmission is in neutral, and the engine is
operating at an acceptable idle speed, such criteria all being
sensed by the electronic control unit 20. If the oil level system
is not enabled, the process 32 simply remains in a hold mode until
enablement occurs.
When the oil level process is engaged as at 34, the output of the
oil level sensor 26 is obtained as at 36 and passed to a filter 38
where the output signals are integrated over time to obtain an
average signal which is accurately indicative of the actual level
and density of oil within the reservoir of the transmission 16
receiving the float of the oil level sensor 26. The filter 38
effectively eliminates signal noise and spurious or extraneous
signals to provide an accurate signal corresponding to actual fluid
level.
At 40, a number of diagnostics of the data signals of FIG. 2 are
undertaken to determine if an oil level determination may be made.
Among the diagnostics is the determination as to whether the output
of the oil level sensor 26 is a legitimate signal as existing
between upper and lower threshold levels. An additional diagnostic
is taken with respect to the oil temperature by monitoring the
output of the temperature sensor 24 to determine if the oil
temperature is within acceptable limits. Engine speed is also
monitored to fall within a particular range to assure that the
engine is at an acceptable idle speed for the test to be
undertaken. As presented above, the engine speed is represented by
the output signal from the transducer 28. In like manner,
diagnostics are undertaken on the output of the transmission speed
transducer 30 to assure that it also falls below a set threshold.
Finally, the diagnostics at 40 also determines whether a
predetermined time period has elapsed from the shifting of the
transmission 16 into neutral to assure sufficient drain back or
settling time for the transmission oil.
At decision block 42, a determination is made as to whether the
data signals satisfy the diagnostic tests at 40 and whether a
sufficient period of time has elapsed from the shifting of the
transmission 16 into neutral. If the diagnostics are not satisfied,
the process continues to loop as shown. If, however, the
diagnostics are satisfied at 42, a first computation is made at 44
as to the density of the transmission oil. As mentioned above, and
as known in the art, the density of transmission oil is a function
of the temperature of the oil. Consequently, the electronic control
unit 20 may simply employ a look-up table to determine the density
of the oil corresponding to the temperature sensed by the
thermistor 24. Since the output of the oil level sensor 26
correlates with the height of the float of the sensor, the same
being a function of the actual level of the oil within the
reservoir and the density of the oil, compensation must be made for
any deviation of the oil density from a nominal value. The
effective volume of the transmission oil within the reservoir is
affected by resultant air entrainment within the oil resulting from
operation of the transmission. At 46, such compensation is made,
determining the effective level of the oil in the reservoir at a
predetermined test density including air entrainment from
transmission operation. Of course, such level is an indication of
volume.
At 48, further compensation must be made for the output signal of
the oil level sensor 26 as impacted by engine speed and settling
time. As will be appreciated by those skilled in the art,
transmission oil level is related to idle speed. Such relationship
is formulated in a look-up table maintained in the memory of the
electronic control unit 20. The signal obtained from the engine
speed transducer 28 may then be employed to compensate or adjust
the data of the output signal of the oil level sensor 26 to a
nominal idle speed such as, for example, 600 rpm. Those skilled in
the art will appreciate that the idle speed of the engine may vary
as a function of many parameters, including the loading of the
engine such as by activation of an air conditioner or other
auxiliary loads.
At 49, further compensation is made for settling time. Once the
transmission 16 is shifted into neutral, the transmission oil
begins to drain into the transmission reservoir where the oil level
sensor 26 is maintained. At the same time, air entrained in the oil
during transmission operation begins to leave the oil. Accordingly,
the actual amount of oil within the reservoir is time dependent as
measured from the neutral shift. The rate at which the oil flows
back to the reservoir is, of course, readily known and,
accordingly, a look-up table may be provided in the electronic
control unit 20 which correlates settling time with the volume of
expected oil to be returned to the reservoir. Again, the settling
time may be temperature dependent such that the look-up table
comprises a family of curves. With the test of the process 32
targeted for a specific settling time, the deviation of settling
time as it impacts the output of the oil level sensor 26 may be
readily compensated from the look-up table.
Having compensated the output signal of the oil level sensor 26 for
changes in temperature-related oil density, engine speed, and
settling time, the corrected signal from the oil level sensor 26 is
thus indicative of an actual oil level within the reservoir under
ideal idling conditions. Any deviation of the adjusted level from a
desired level is evidenced by an error at 50. Since the operations
at 46, 48, and 49 are directed toward determining oil level in a
lineal measurement such as millimeters, the error determined at 50
is calculated in such lineal dimensions and then converted to
volume. The error is preferably determined in a readily
recognizable unit of measure such as pints or the like. This error
may be indicative of an absence of adequate transmission fluid
within the reservoir, or the presence of excessive fluid.
As presented above, those skilled in the art readily appreciate
that oil density is temperature dependent. Accordingly, the volume
of the oil within the reservoir of the transmission 16 is also
temperature dependent. Accordingly, it is necessary at 58 to
compensate for any volume change between the actual temperature at
which the oil level is measured and the typical operating
temperature of the oil. As shown in FIG. 3, the temperature of the
oil as sensed by the thermistor 24 is continually monitored as at
52 during the entire period of operation of the transmission 16.
The temperature signals are passed through an appropriate filter 54
and are integrated or otherwise averaged as at 56 so that a
characteristic operating oil temperature may be determined as at
56. Since it is likely that the temperature of the oil at the time
of the test differs from the average operating temperature of the
oil, it is necessary at 58 to compensate for the difference in
temperature and, accordingly, for the resultant difference in the
error as determined at 50. If the test temperature and typical
operating temperature are the same, then the error determined at 50
will be accurate. However, if the test temperature is higher or
lower than the average operating temperature, then adjustment is
necessary to the error determination at 50 such that the amount of
oil added to or released from the transmission 16 will be
appropriate. The amount of correction is obtained from a look-up
table at 58 which is calibrated to acknowledge the thermal
expansion for the design volume of the reservoir of the
transmission in question. A calculation is made at 60 as to the
temperature-compensated level reading and resultant error. This
information may be employed by the operator to take appropriate
corrective action to add oil to or remove oil from the transmission
reservoir.
A display of the compensated oil level and/or error determination
may be requested by the operator as at 61 to allow the operator to
take appropriate corrective action. Such a request may be made by
an appropriate switch or the like. When such a request is made an
appropriate display is made as at 62 on a read-out device such as
an LED or liquid crystal device. If no display is requested, the
process 32 simply loops to begin anew.
It will be appreciated that the compensation for temperature
deviation made at 58 could be employed between the operations of 49
and 50. In other words, such temperature compensation could be made
to adjust the level determination before the volume error
calculation at 50, or it may be employed as described above and
shown in the drawing. In either event, compensation for deviation
from typical operating temperatures is made.
It should now be appreciated that the concept of the invention is
operable to accurately measure transmission oil levels and to
compensate the measured level for deviations from optimal test
conditions. Such compensation may be made on the basis of the
deviation of the oil temperature from a nominal test temperature,
or similar deviations of engine speed and settling time. The output
signal from the oil level sensor 26 is first compensated to adjust
for changes in oil density resulting from deviations in the oil
temperature from nominal desired test conditions, then the oil
level and error is adjusted to compensate for the deviations just
described. Consequently, each test or measurement is effectively
made at ideal test conditions, for compensation is made for any
deviation from such ideal conditions.
Thus it can be seen that the objects of the invention have been
satisfied by the structure and method presented above. While in
accordance with the patent statute only the best mode and preferred
embodiment of the invention has been presented and described in
detail, it is to be understood that the invention is not limited
thereto or thereby. Accordingly, for an appreciation of the true
scope and breadth of the invention reference should be made to the
following claims.
* * * * *